The measurement results of blood flow and perfusion imaging technologies are typically disrupted by a motion artifact of the target tissue/organ in clinical circumstances. This movement can be micro (i.e., pulsatility of an arteriole due to systole and diastole blood pressure levels), intermediate (i.e., normal peristalsis of the small or large bowel) or macro (i.e., the movement of the heart during the cardiac cycle). This movement can be intrinsic to the imaged tissue (i.e., examples cited above), or extrinsic (i.e., the movement of the heart as a result of the movement of the lungs during ventilation). Thus, in many clinical situations, where accurate quantification of flow and perfusion is desirable, keeping the imaging target in a stationary status is difficult and, in some clinical scenarios, is not even possible. For example, such as imaging the distributions of blood flow velocity and flow rate for quantifying perfusion in coronary arteries and myocardium of a beating heart. Unfortunately, most conventional laser-based perfusion technologies either assume the target tissue/organ is stationary, which introduces significant inaccuracy or error in the clinical measurement of blood speed or velocity where the target is moving, such as a beating heart, or are simply provide no information for quantification of perfusion in terms of blood flow rate distribution that is critically needed in the clinical situation where the target may or may not be moving.
Tissues/organs in animals or human respond differently to light of different wavelengths. In general, light of shorter wavelengths can penetrate only the superficial layers of the tissues while light of longer wavelengths can penetrate both superficial layers and sub-surface layers in the spectral region from ultraviolet (UV) to near-infrared (NIR). UV and visible light of wavelengths less than, for example, 550 nm is optimal for detailed anatomic visualization in medicine when viewing the surface of tissues and organs. However, unlike NIR light, UV or visible light imaging is usually not inherently capable of revealing the physiological characteristics of tissues/organs in sub-surface layers, in part due to lack of penetration of the tissues/organs. Accordingly, improved methods of visualization and quantification are desired.